Radio Frequency Identification (RFID) has become an important implementation of an Automatic Identification technique. The object of any RFID system is to carry data suitable transponders, generally known as tags, and to retrieve data, by machine-readable means, at a suitable time and place to satisfy particular application needs. Data within a tag may provide identification for an item in manufacture, goods in transit, a location, the identity of a vehicle, an animal or individual. By including additional data the prospect is provided for supporting applications through item specific information or instructions immediately available on reading the tag. For example, the color of paint for a car body entering a paint spray area on the production line, the set-up instructions for a flexible manufacturing cell or the manifest to accompany a shipment of goods.
RFID technologies vary widely in frequency, packaging, performance, and cost. There are many established applications. A system requires, in addition to tags, a means of reading or interrogating the tags and some means of communicating the data to a host computer or information management system. A system will also include a facility for entering or programming data into the tags, if this is not undertaken at source by the manufacturer.
Communication of data between tags and a reader is by wireless communication. Two methods distinguish and categorize RFID systems, one based upon close proximity electromagnetic or inductive coupling and one based upon propagating electromagnetic waves. Coupling is via ‘antenna’ structures forming an integral feature in both tags and readers. While the term antenna is generally considered more appropriate for propagating systems it is also loosely applied to inductive systems.
Transmitting data is subject to the influences of the media or channels through which the data has to pass, including the air interface. Noise, interference and distortion are the sources of data corruption that arise in practical communication channels that must be guarded against in seeking to achieve error free data recovery. Moreover, the nature of the data communication processes, being asynchronous in nature, requires attention to the form in which the data is communicated. Structuring the bit stream to accommodate these needs is often referred to as channel encoding and although transparent to the user of an RFID system the coding scheme applied appears in system specifications. Various encoding schemes can be distinguished, each exhibiting different performance features.
To transfer data efficiently via the air interface or space that separates the two communicating components requires the data to be superimposed upon a rhythmically varying (sinusoidal) field or carrier wave. This process of superimposition is referred to as modulation, and various schemes are available for this purposes, each having particular attributes that favor their use. They are essentially based upon changing the value of one of the primary features of an alternating sinusoidal source, its amplitude, frequency or phase in accordance with the data carrying bit stream. On this basis one can distinguish amplitude shift keying (ASK), frequency shift keying (FSK) and phase shift keying (PSK). Based on these limitations, the operational distance for inductively coupled RFID tags such as those operating at 125 kHz and 13.56 MHz cannot be greater than approximately 5 inches when the reader and antenna are fully integrated into a small hand-held mobile computer.
Nevertheless, many applications require hand-held readers that will be capable of interrogating RFID tags at distances beyond 12 inches. The operational distance for inductively coupled RFID tags such those operating at 125 kHz and 13.56 MHz are directly proportional to the antenna (coil) size. For example, a typical design will generally provide interrogation distances between 35% to 200% of the antenna loop diameter. Therefore, in order to obtain 12 inches of read range on a typical credit card size RFID tag, the antenna can be approximately six inches in diameter at best. Integrating such a large antenna will grow the size of the hand-held mobile computer to a point where it is no longer practical for use over an extended period of time.
Even if such a large antenna were integrated, it must be maximally separated from the metallic parts within the mobile computer so as to avoid magnetic field dampening. Examples of metallic parts are scan engine opto-mechanical chassis, mounting brackets, electronic packaging, flex connectors, electromagnetic shielding, etc. In addition, a large battery will be necessary in order to sustain an adequately large current in the RFID antenna that will generate the required magnetic field strength for interrogating tags out to the desired distances.
The three key requirements of maximally large antenna, clearance from metallic components, and high current generating capability over the operational life of the device make it impractical under current design restraints to construct a small and ergonomically correct mobile computer.
There is, therefore, a need in the art for an apparatus, method, and system that will enable a hand held mobile computer to use RFID for distances from beyond about 12 inches while still maintaining its ergonomic correctness.